Electronic systems typically use a timing signal from a timing source, e.g., a pulse train generated by a clock circuit, to coordinate the interoperation of various electronic circuits within the system. For example, this timing signal is used to coordinate the passing of data through the system and to initiate various procedures that operate on the data. To improve the reliability of such systems, a back-up timing source is typically included. The back-up timing source is used when, for example, the main timing source fails or is removed from the system for maintenance.
Telecommunications systems are being designed to operate at increasingly higher speeds. Unfortunately, in conventional telecommunications systems, data is often lost when the system switches between the primary timing source and the back-up timing source. This is referred to in the industry as a "hit" during the switch. The hit is caused by phase differences between the primary and back-up timing sources. As the system speeds increase, the amount of data lost during a switch over to the back-up timing source can cause unacceptable levels of lost data that need to be retransmitted.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a system that can switch between primary and back-up timing sources without an unacceptable hit on the data transmitted by the system.